Thanks everyone for the replies and ideas both on and off list. Based on your input, next week when the system is in Float I plan to have the class isolate the faulty battery and measure voltage, let it rest for a couple days, then load test at about C/10. Predicted result is that it will show extremely low amp-hour capacity. Since the other battery in the string will then be isolated also, we will load test it at the same time to compare. Best regards and thanks again;
Dan Fink Adjunct Professor, Ecotech Institute IREC Certified Instructor™ for: ~ PV Installation Professional ~ Small Wind Installer Executive Director, Buckville Energy NABCEP Accredited Continuing Education Providers™ 970.672.4342 On Tue, Nov 24, 2015 at 7:30 AM, Drake <[email protected] > wrote: > Having one cell die seems to be an emerging pattern. > > > At 09:49 AM 11/22/2015, you wrote: > > Esteemed Wrenches; > > I'm looking for input on what could be going on with a battery bank at the > college I teach for. It's a stand-alone system with 4 Trojan 12v T-1275 in > series / parallel for 24v, 660w of PV, running only a drainback solar hot > water system for space heating. So, 3 pumps and 3 DTCs, max load 100 watts > and doesn't run all that often, outback CC is usually in float. The > batteries are only 2.5 years old and are regularly maintained. > > My lab class tested and maintained the battery bank last week, and on one > battery there was one cell, in the middle of the battery, with a SG so low > it wouldn't even register on our refractometer or midnite hydrometer. That > battery reads about 0.2v lower than the others. All the other cells in that > battery read reasonable SG, with 2 cells on the downstream side reading SG > slightly low, but still in reasonable range. This was of course all before > topping up the electrolyte with distilled water. > > Our troubleshooting exercise looked at: > ~ Measurement error? Nope, I was right there supervising and 2 different > lab classes got the same results with 2 different instruments; > ~ Stratification? A suspicion especially since the system is usually in > float. We equalized twice, no change in SG. I DID hear that likely this was > the first time the batteries had ever been equalized, but no way to know > for sure. > ~ Spilled electrolyte from tipped battery replaced with water by a > previous instructor's class? Can't see this, all the other cells would have > lost electrolyte too; > ~ A student accidentally discharged electrolyte into the bucket instead of > back in the cell, then was replaced by distilled water when topping up? I > can't see that either, the midnite hydrometer needs only a small sample. > > So, I'm left with "likely we have a cell that is failing for some reason" > and students secretly smug that the professor is also stumped. > > Any ideas? > > > Dan Fink > Adjunct Professor, Ecotech Institute > IREC Certified Instructor™ forr:Â > ~ PV Installation Professional > ~ Small Wind Installer > Executive Director, Buckville Energy > NABCEP Accredited Continuing Education Providers™ > 970.672.4342 <970..672.4342> > > Â > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/[email protected]/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/[email protected]/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > >
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